The present invention relates to the froth flotation of finely-divided coal particles for separation of ash therefrom and more particularly to a new promoter which enhances the coal recovery in the froth flotation process.
Coalification is a natural process which results in the deposits of combustible carbonaceous solids in combination with some non-combustible mineral matter. Most coal cleaning is carried out by gravity separation methods utilizing jigs, shaking tables, heavy media or cyclones, and like techniques. The fine coal therefrom has been incorporated into clean coal or simply discarded in the past; however, due to economic and environmental considerations gained by recovery of the fine coal fraction, fine coal beneficiation has become a necessity in most coal operations requiring any degree of preparation. Froth flotation is one method which has been practiced for cleaning the fine coal.
The use of froth flotation to effect a separation of pyritic sulfur and ash particles from coal can be achieved only if liberation of these unwanted particles from the coal has taken place. Most high-grade coals are floatable naturally due to their hydrophobic surface and typically only require a frothing agent for effecting flotation. A frothing agent imparts elasticity to the air bubble, enhances particle-bubble attachment so that the coal is buoyed to the surface of the slurry. The flotability of coal can vary within a given seam at a mine depending upon the exposure of the locale to weathering elements or the blending of coals from different seams. Butuminous and lower grade coals either possess an oxidized condition as mined or undergo oxidation (weathering) when the coal is stored or stockpiled for later processing. Coal that has been oxidized does not respond well to froth flotation. As the degree of oxidation increases, coal becomes increasingly hydrophilic and, therefore, less coal readily can be floated. Heretofore, oxidized coal which was not floatable was discarded in the tailing of the flotation process with little attempt to recover this loss being undertaken.
Recently, though, technology has emerged for practicing froth flotation of oxidized and other difficult to float coal particles. For example, U.S. Pat. No. 4,253,944 shows a promoter which is the condensation product of a fatty acid or fatty acid ester with an ethoxylated or propoxylated amine. U.S. Pat. No. 4,308,133 shows a promoter which is an aryl sulfonate. European patent application Publication No. 16914, Oct. 15, 1980, shows a promoter which is an alkanol amine-tall oil fatty acid condensate. U.S. Pat. No. 4,305,815 shows a promoter which is a hydroxy alkylated polyamine. U.S. Pat. No. 4,278,533 shows a promoter which is a hydroxylated ether amine. U.S. Pat. No. 4,196,092 shows a conditioning agent of a frother and a bis(alkyl)ester of a sulfosuccinic acid salt. United Kingdom Pat. No. 2,072,700 (and corresponding U.S. Pat. No. 4,340,467) floats coal with a latex emulsion prepared from a hydrocarbon oil with a hydrophobic water in oil emulsifier and a hydrophilic surfactant. Canadian Pat. No. 1,108,317 shows anionic surfactants which are fatty sulfosuccinates. Russian Inventor's Certificate No. 882,626 proposes a collector-frother which is an hydroxy, chloro or sulfide derivative of the methyl or ethyl ester of caproic acid.
Polish Pat. No. 104,569 proposes the use of ethoxylated higher fatty acids in coal flotation. U.S. Pat. No. 2,099,120 proposes the use of a water-soluble salt of a mono-ester of an organic dicarboxylic acid to float coal. British Pat. No. 741,085 proposes the flotation of coal by using salts of napthenic acids, cresylic acids, or rosin acids as wetting agents.
The foregoing art is consistent with accepted coal flotation principles that emulsified reagents should be used in coal froth flotation. While such promoters in the art can function in the coal flotation process, there is need for improving coal recoveries and improving the quality of the recovered coal. The present invention provides such improved high coal recoveries with improvements in coal quality utilizing a promoter which is highly effective and less expensive.